2. amps-preamps
  3. 140029-80294

Does anyone care to ask an amplifier designer a technical question? My door is open.

I closed the cable and fuse thread because the trolls were making a mess of things. I hope they dont find me here.

I design Tube and Solid State power amps and preamps for Music Reference. I have a degree in Electrical Engineering, have trained my ears keenly to hear frequency response differences, distortion and pretty good at guessing SPL. Ive spent 40 years doing that as a tech, store owner, and designer.
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Perhaps someone would like to ask a question about how one designs a successfull amplifier? What determines damping factor and what damping factor does besides damping the woofer. There is an entirely different, I feel better way to look at damping and call it Regulation , which is 1/damping.

I like to tell true stories of my experience with others in this industry.

I have started a school which you can visit at http://berkeleyhifischool.com/ There you can see some of my presentations.

On YouTube go to the Music Reference channel to see how to design and build your own tube linestage. The series has over 200,000 views. You have to hit the video tab to see all.

I am not here to advertise for MR. Soon I will be making and posting more videos on YouTube. I don’t make any money off the videos, I just want to share knowledge and I hope others will share knowledge. Asking a good question is actually a display of your knowledge because you know enough to formulate a decent question.

Starting in January I plan to make these videos and post them on the HiFi school site and hosted on a new YouTube channel belonging to the school.


128x128ramtubes
ramtubes's avatar
ramtubes OP
460 posts
 
@terry9 

Each Quad has its own mono block. Two Quads facing ahead, and two Quads at one radian angles, facing in. A bit like one of Walker's experiments. Think of two sides of a hexagon on the left, mirror image on the right. And two at the back of the room, attenuated, but important.


Its ok, ive seen plenty of SS amps. The negative temp coefficient is interesting. 

You sure have a lot of stuff there. It would still like to know what kind of capacitance you are driving at 10Khz and up. 

As to the capacitor question. In the passband there is 0 Volts of signal across the cap. 

I'm still in the Polypropylene camp. Best thing for the money. Remember any part I buy is 5 x cost to the final buyer. So I cant buy too many $50 caps expensive resistors. I also appreciate manufacturers who make relaible parts. I have found CJ, Jensen, and others to fail. There is no reason for a coupling cap to fail in this day. The problem with premium caps it the people make them do not have the years of experience that the old timers have.

While I could make an amp with all premium parts, sell it for a lot more, I just dont find anything special about these parts. I would only do it to reach into the buyers pocket.
ramtubes's avatar
ramtubes OP
460 posts
 
@terry9

Are you aware that the secondary capacitance of this transformer is 800 pf and the input capacitance of the speaker panel is many times lower? If I multiply that times turns ratio squared i get a primary load of 45 Microfarads. For the transformer alone.  Are they kidding? Thats a lot to drive. The QUAD transformers are quite good and much lower capacitance. 

I dont get these Plitrons at all. Tell me what is wrong with the QUAD transformers?

The primary of the Plitron is 0.1 ohm. How low is your dc offet?


donjr
1,335 posts
 
In general, your thoughts on Accuphase integrated amps? Do I need to post specs?

georgehifi's avatar
georgehifi
10,312 posts
 
ramtubes OP
One thing to do is follow John Atkinson’s measurements of amplifiers. If you dont, get Stereophile its a good mag and only $12-15 a year.

This is great advise for those here, to learn and understand these Stereophile measurements, it’s crucial to giving good informed advise to others, and to selecting the right stuff for even for themselves.

As all decent manufactures use these types of measurements to design build and to test their products as well as all the EE laws that go with them. Anyone who doesn’t use or doesn’t believe in them, should be given a very wide berth as they have no idea what they’re talking about.

Cheers George
terry9
2,348 posts
 
Agreed that polypropylene is best for the money. Improvements on polyp are incremental and absolutely not worth it - unless you are a hobbyist who wants to see how far he can go, just because. 

What I see in Plitron (theoretically) is two things: first, the two plates of the ESL are driven by the same core, so they can be precisely balanced; and second, they offer 75:1 step-up instead of 250:1. Since I committed to 75:1 with 25V rails, going back to 250:1 would involve re-engineering the protection circuits.

Rather than that, I would try to build high voltage amps to drive the Quads directly. Wish me luck - and long life!

What I hear (subjectively) is that the Plitron 2905's are much brighter than the remaining stock 2905, without sounding harsh. Piano on vinyl sounds quite similar to the instrument upstairs on the modified units. The unmodified unit sounds mellow but imprecise compared to the Plitronned. In fairness I must add that this was accomplished with the help of nichrome wire and a small inductor to equalize primary impedance over the frequency band, as per the Vandersteen data sheets.

My DC offset used to be 50mV or less. What it is now is a good question, one that you have prompted me to ask. Thank you.
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